Dilute juice beverage products are well known in the art. One component that is desirably present in dilute juice beverages that are intended to be stored without refrigeration (e.g., at ambient temperatures) is an antimicrobial preservative. Dilute juice beverages, when exposed to food spoilage microorganisms, can provide a hospitable environment for rapid microbial growth. Such exposure can, and infrequently does, result from accidental inoculation of the dilute juice beverage with these microorganisms during manufacturing or packaging. Food spoilage microorganisms can then rapidly proliferate by feeding on nutrients provided by the juice component of the dilute juice beverage.
Preservatives, such as sorbates, benzoates, organic acids, and combinations thereof have been used in dilute juice beverages to provide some degree of microbial inhibition. At levels effective to inhibit microbial growth, some of these preservatives can contribute off-flavors to dilute juice beverages. For example, accepted usage levels for potassium sorbate can be in the range of from about 200 to about 3000 ppm. Typically, potassium sorbate is included in dilute juice beverages at levels far above the effective minimum to ensure antimicrobial activity. However, at the higher end of this accepted usage range, potassium sorbate can contribute off-flavors to dilute juice beverages.
In addition, potassium sorbate is not effective against certain yeasts that can be present in beverage processing plants. Of particular concern is Zygosaccharomyces bailii. Zygosaccharomyces bailii is a common food spoilage yeast that is extremely resistant to weak acid preservatives such as potassium sorbate, tolerating in some cases preservative concentrations well in excess of those permitted legally. See Cole et al, "Probability of Growth of the Spoilage Yeast Zygosaccharomyces bailii in a Model Fruit Drink System," Food Microbiology, 1987, 4, pp. 115-19. See also Warth, "Transport of Benzoic and Propanoic Acids by Zygosaccharomyces bailii," Journal of General Microbiology, 1989, 135, pp. 1383-90 (Zygosaccharomyces bailii very tolerant of common weak-acid-type preservatives, including sorbic acids). This yeast can enter the beverage plant by means of unpasteurized or recontaminated chemically preserved fruit juice and then establish itself in various portions of the plant's equipment, leading to further contamination and spoilage.
Yeast and mold inhibitors such as natamycin have been found to be particularly effective against yeasts such as Zygosaccharomyces bailii. See Shirk & Clark, "The Effect of Pimaricin in Retarding the Spoilage of Fresh Orange Juice," Food Technology, 1963, p 108. Natamycin is also effective against a variety of other saprophytic and parasitic fungi and yeasts. See U.S. Pat. No. 3,892,850 (Struyk), issued Jul. 1, 1975. However, natamycin, when in solution, is rather unstable. Inactivation of natamycin by light, peroxides or oxygen proceeds at the fastest rate in solution or suspension. For example, an aqueous solution of 6 mcg/ml of natamycin becomes microbiologically inactive after twenty-four hour exposure to light. Natamycin is also sensitive to heavy metals, and can lose up to 75% of its effectiveness in four or five hours in the presence of these heavy metals. In addition, natamycin is not effective against bacteria. See U.S. Pat. No. 4,536,494 (Carter), issued Aug. 20, 1985.
Dialkyl dicarbonates have also been used or suggested for use as yeast inhibitors in wine, ready-to-drink teas, fruit juices, vegetable products, pharmaceutical products, beer and the like. See 37 CFR .sctn.172.133. See also U.S. Pat. No. 3,979,524 (Bayne), issued Sep. 7, 1976 and U.S. Pat. No. 2,910,400 (Berhard et al), issued Oct. 27, 1959 (also referred to as "pyrocarbonic acid esters"). Dialkyl dicarbonates provide a very effective initial "kill" of any microorganisms in the just formulated single strength beverage. However, the dialkyl dicarbonate is rapidly hydrolyzed by aqueous systems such as dilute juice beverages shortly after addition. As the concentration of dialkyl dicarbonate decreases, it soon becomes ineffective to kill microorganisms that might be introduced later during processing into the beverage. See Ough, "Dimethyldicarbonate and Diethyldicarbonate" Antimicrobials in Foods, 193, Marcel Dekker, pp. 343-368.
It has been recently suggested that the use certain food grade polyphosphates, especially sodium hexametaphosphate, can enhance the potency of preservatives, such as potassium sorbate, when the preservative is used at lower levels in dilute juice beverages. See U.S. Pat. No. 5,431,940 (Calderas), issued Jul. 11, 1995, which discloses the use of polyphosphates, such as sodium hexametaphosphate, with sorbate preservatives, such as potassium sorbate, in dilute juice beverages having relatively low water hardness. However, inclusion of these polyphosphates can present problems in beverages fortified with calcium or containing proteins, especially milk proteins such as the caseins and albumins. The inclusion of polyphosphates at levels sufficient to potentiate the preservative will also sequester any calcium and milk proteins present and precipitate out the resulting complexes.
Even when preservatives such as potassium sorbate are included, dilute juice beverages can still require refrigeration to maintain microbial stability. Refrigerated beverages require special handling, especially in terms of shelf space in the store. This also necessitates more expensive refrigeration trucks and railroad cars in transporting these beverages to the stores.
Accordingly, it would be desirable to be able to provide dilute juice beverages that: (1) use preservative systems that can be formulated with existing antimicrobials such as potassium sorbate; (2) are stable against microbial growth at ambient temperatures, including yeasts such as Zygosaccharomyces bailii; (3) do not have off-flavors contributed by the preservative system; (4) can be fortified with calcium; (5) can include milk solids; (6) do not require special handling, especially refrigeration, during transportation and storage.